1. Field of the Invention
The present invention relates to a hybrid working machine wherein a rotating shaft of a generator-motor and that of a hydraulic pump are coupled directly by spline coupling.
2. Description of the Related Art
A background technique will be described below with reference to an excavator as an example.
FIG. 3 shows a configuration example of a hybrid excavator.
A generator-motor 1 adapted to perform both generator function and motor function and a hydraulic pump 2 serving as an oil pressure source of hydraulic actuators are connected in tandem to an engine 3 and pressure oil from the hydraulic pump 2 is supplied to plural hydraulic actuators through a control valve 4.
On the other hand, a battery (an electric power storage device) 6 is charged through an inverter 5 by the generator function of the generator-motor 1 and at the same time, with the electric power stored in the battery 6, the generator-motor 1 performs the motor function to assist the engine 3 (see Japanese Patent Laid-Open No. 2001-12274).
A rotating shaft of the generator-motor 1 and that of the hydraulic pump 2 are coupled directly by spline coupling and rotate integrally with each other by operation of the engine.
In the direct coupling structure by spline coupling it is known that there occurs fretting wear (wear caused by striking of spline teeth against each other under fine vibration) by revolution fluctuation.
Particularly in the spline coupling structure between the generator-motor 1 and the hydraulic pump 2, fretting wear is apt to occur because there is torque fluctuation in generator function/motor function of the generator-motor 1 in addition to the revolution fluctuation of the engine 3.
A method conceivable as a countermeasure to the fretting wear is to fix the spline coupling portion so as to prevent vibration. However, this fixing method is not suitable for practical use because not only the assembling performance is deteriorated but also a difficulty is encountered in ensuring a required space and the cost becomes high.
On the other hand, it is known that the fretting wear can be suppressed by lubricating the spline coupling portion with oil.
In this connection, the following methods are considered as concrete methods.
(I) An external oiling method wherein an oiling hole communicating with the spline coupling portion is formed in a casing of the generator-motor 1 and, where required, lubricating oil is fed through the oiling hole to the spline coupling portion from the exterior.(II) An oil sealing method wherein an oil chamber communicating with the spline coupling portion is formed in the casing and lubricating oil is sealed into the oil chamber to immerse the spline coupling portion within the lubricating oil.
However, the external oiling method requires maintenance and there easily occurs deficient lubrication due to forgetting to supply oil or oil shortage. Thus, the reliability of wear prevention is low.
Further, in the oil sealing method, not only the oil sealing work after assembly is troublesome, but also there is a fear of deficient lubrication due to deterioration or change in quality of oil.